Dual-Particle Aqueous Fe/Ni Semi-solid Flow Batteries With High Energy Density and Halved Energy Cost Enabled by Electrolyte Modulation

Semi-solid flow batteries (SSFBs) break traditional solubility limits, yet sluggish electrochemical kinetics, parasitic hydrogen evolution, and high slurry viscosity severely restrict their practical energy density and cycling life. Herein, a dual-particle aqueous Fe/Ni SSFB is present that utilizes low-cost Fe₂O₃ and Ni(OH)₂ particles as anode and cathode active materials, respectively. Through systematic electrolyte engineering, the bottlenecks of electrochemical performance and electrolyte viscosity are simultaneously addressed. Specifically, redox targeting is introduced to boost cathode kinetics, with trace additives concurrently suppressing anodic hydrogen evolution, enabling a 10 wt% Fe/Ni achieves an energy density boost from 3 to 21 Wh L^-1, along with stable operation for 100 cycles. To break the viscosity-loading trade-off, functional dispersants are employed to halve the electrolyte viscosity. This breakthrough enables stable operation at 30 wt% solid loading, yielding an energy densities of 58 Wh L^-1 at 10 mA cm^-2 (6.7-fold higher than dispersant-free), which outperform the reported aqueous metal-based SSFBs in literature. Benefiting from the use of low-cost active materials and trace additives, the energy cost is merely 24 US$ kWh^-1 (vs ≥48 US$ kWh^-1 for reported SSFBs). This study provides a paradigm shift toward economically viable and high-performance SSFBs.